C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  how to write an operator          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Martin Vorbrodt Guest Posted: Sat Aug 28, 2004 8:47 pm    Post subject: how to write an operator which is preferable and WHY? class Complex { .... friend Complex operator + (const Complex& lhs, const Complex& rhs); OR friend const Complex operator + (const Complex& lhs, const Complex& rhs); OR either one but a member operator instead of a friend. Thanx, Martin Back to top Phlip Guest Posted: Sat Aug 28, 2004 10:09 pm    Post subject: Re: how to write an operator Martin Vorbrodt wrote: Quote: which is preferable and WHY? class Complex { ... friend Complex operator + (const Complex& lhs, const Complex& rhs); OR friend const Complex operator + (const Complex& lhs, const Complex& rhs); ^ That const adds no value, and there are those who claim it interferes with certain type-specific operations. If you meant 'Complex const &', don't do that either, because functions generally should not return value-types by reference. Quote: OR either one but a member operator instead of a friend. A member operator might not balance properly: 5 + Complex(8, 2); -- Phlip http://industrialxp.org/community/bin/view/Main/TestFirstUserInterfaces Back to top DaKoadMunky Guest Posted: Sun Aug 29, 2004 1:30 am    Post subject: Re: how to write an operator Quote: That const adds no value Well, if you believe what some people say about operator overloading and "do as the ints do" then it does make it behave more like a function that returns a built-in type by value. int a,b,c; (a+b) = c; //This should not compile Complex a,b,c; (a+b) = c; //This will compile if return value is not const. For reasons I have never grasped a user-defined type returned by value is not an lvalue yet it can be the target of modifying operations. To make the overloaded operator behave in a way analagous to the built-in operators you must make the return value const. Does this have value? I don't know. Back to top Siemel Naran Guest Posted: Sun Aug 29, 2004 4:29 am    Post subject: Re: how to write an operator "DaKoadMunky" <dakoadmunky (AT) aol (DOT) com> wrote in message Quote: Phlip friend const Complex operator + (const Complex& lhs, const Complex& rhs); Quote: That const adds no value Well, if you believe what some people say about operator overloading and "do as the ints do" then it does make it behave more like a function that returns a built-in type by value. int a,b,c; (a+b) = c; //This should not compile Complex a,b,c; (a+b) = c; //This will compile if return value is not const. For reasons I have never grasped a user-defined type returned by value is not an lvalue yet it can be the target of modifying operations. To make the overloaded operator behave in a way analagous to the built-in operators you must make the return value const. Does this have value? I don't know. Yes, it prevents accidentally modifying a newly returned object, so might catch code which compiles but may do the wrong thing. a++ = b; Back to top Peter Koch Larsen Guest Posted: Sun Aug 29, 2004 1:56 pm    Post subject: Re: how to write an operator "Martin Vorbrodt" <mvorbrodt (AT) poczta (DOT) onet.pl> skrev i en meddelelse news:cgqr01$567$1 (AT) news (DOT) onet.pl... Quote: which is preferable and WHY? class Complex { ... friend Complex operator + (const Complex& lhs, const Complex& rhs); OR friend const Complex operator + (const Complex& lhs, const Complex& rhs); OR either one but a member operator instead of a friend. Thanx, Martin You should prefer class Complex { Complex& operator+=(Complex const& rhs); ...... then you can have: Complex operator +(const Complex lhs,Complex const& rhs) { return lhs += rhs; } Back to top Martin Vorbrodt Guest Posted: Sun Aug 29, 2004 3:15 pm    Post subject: Re: how to write an operator So how about +=, etc operators. I assume they return a reference, not a constant referance, since this code is legal and works just fine: int a = 1, b = 2, c = 3; a += b += c; (a += b) += c; a += (b += c); "DaKoadMunky" <dakoadmunky (AT) aol (DOT) com> wrote Quote: That const adds no value Well, if you believe what some people say about operator overloading and "do as the ints do" then it does make it behave more like a function that returns a built-in type by value. int a,b,c; (a+b) = c; //This should not compile Complex a,b,c; (a+b) = c; //This will compile if return value is not const. For reasons I have never grasped a user-defined type returned by value is not an lvalue yet it can be the target of modifying operations. To make the overloaded operator behave in a way analagous to the built-in operators you must make the return value const. Does this have value? I don't know. Back to top Martin Vorbrodt Guest Posted: Sun Aug 29, 2004 3:16 pm    Post subject: Re: how to write an operator Why would i want to do that? That would modify LHS variable. I don't want that. "Peter Koch Larsen" <pklspam (AT) mailme (DOT) dk> wrote Quote: "Martin Vorbrodt" <mvorbrodt (AT) poczta (DOT) onet.pl> skrev i en meddelelse news:cgqr01$567$1 (AT) news (DOT) onet.pl... which is preferable and WHY? class Complex { ... friend Complex operator + (const Complex& lhs, const Complex& rhs); OR friend const Complex operator + (const Complex& lhs, const Complex& rhs); OR either one but a member operator instead of a friend. Thanx, Martin You should prefer class Complex { Complex& operator+=(Complex const& rhs); ..... then you can have: Complex operator +(const Complex lhs,Complex const& rhs) { return lhs += rhs; } Back to top Siemel Naran Guest Posted: Sun Aug 29, 2004 4:06 pm    Post subject: Re: how to write an operator "Martin Vorbrodt" <mvorbrodt (AT) poczta (DOT) onet.pl> wrote Quote: "Peter Koch Larsen" <pklspam (AT) mailme (DOT) dk> wrote in message You should prefer class Complex { Complex& operator+=(Complex const& rhs); ..... then you can have: Complex operator +(const Complex lhs,Complex const& rhs) { return lhs += rhs; } That's assuming we want both operators, which is a reasonable assumption. Quote: Why would i want to do that? That would modify LHS variable. I don't want that. It's fine. Look closely at the function arguments. The function receives lhs by value, so it's a copy. However, it should be declared not const. This should suffice. Complex operator +(Complex lhs,Complex const& rhs) { return lhs += rhs; } You can optionally return a const Complex, as indicated in the other sub-thread to prevent accidental assignment to the returned unnamed temporary. const Complex operator +(Complex lhs,Complex const& rhs) { return lhs += rhs; } Back to top Siemel Naran Guest Posted: Sun Aug 29, 2004 4:09 pm    Post subject: Re: how to write an operator Quote: "DaKoadMunky" <dakoadmunky (AT) aol (DOT) com> wrote in message "Martin Vorbrodt" <mvorbrodt (AT) poczta (DOT) onet.pl> wrote We prefer if you reply to posts in place, that is include the quoted text then your comments to that quoted text, then more quoted text. This makes it easier for people to read. At work of course, I usually just hit the reply button as it's faster. Quote: int a,b,c; (a+b) = c; //This should not compile So how about +=, etc operators. I assume they return a reference, not a constant referance, since this code is legal and works just fine: int a = 1, b = 2, c = 3; a += b += c; (a += b) += c; a += (b += c); In return a const object, we're talking about returned a value. Of course, returning a reference to an object is another story. We have to return a non-const or const reference as appropriate to the design. As for returning an object by value, as with operator++ operator+, it doesn't really matter whether we return the object as const or not, but returning const is a little safer and could catch strange bugs. Back to top Peter Koch Larsen Guest Posted: Tue Aug 31, 2004 7:05 am    Post subject: Re: how to write an operator "Martin Vorbrodt" <mvorbrodt (AT) poczta (DOT) onet.pl> skrev i en meddelelse news:cgsrv4$qam$1 (AT) news (DOT) onet.pl... Quote: Why would i want to do that? That would modify LHS variable. I don't want that. Because you almost certainly wants the operator+=. For users of your class it will be confusing if they can write a = a + b but not a += b. As you can see from my code, this makes operator+ very easy to write - and it does not have to be a friend function. Also i must add that i find your reply quite confusing. Do not toppost. Kind regards Peter Quote: "Peter Koch Larsen" <pklspam (AT) mailme (DOT) dk> wrote in message news:pglYc.41619$Vf.2198766 (AT) news000 (DOT) worldonline.dk... "Martin Vorbrodt" <mvorbrodt (AT) poczta (DOT) onet.pl> skrev i en meddelelse news:cgqr01$567$1 (AT) news (DOT) onet.pl... which is preferable and WHY? class Complex { ... friend Complex operator + (const Complex& lhs, const Complex& rhs); OR friend const Complex operator + (const Complex& lhs, const Complex& rhs); OR either one but a member operator instead of a friend. Thanx, Martin You should prefer class Complex { Complex& operator+=(Complex const& rhs); ..... then you can have: Complex operator +(const Complex lhs,Complex const& rhs) { return lhs += rhs; } Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.